package com.freedy.concurrent.Monitors.reentrantLock;

import com.freedy.concurrent.Monitors.Sleeper;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.locks.ReentrantLock;

/**
 * 哲学家就餐问题使用可重入锁进行优化
 * 防止发生死锁
 *
 * @author Freedy
 * @date 2021/4/22 21:03
 */
public class PhilosopherDinner {
    public static void main(String[] args) {
        Chopstick c1 = new Chopstick("1");
        Chopstick c2 = new Chopstick("2");
        Chopstick c3 = new Chopstick("3");
        Chopstick c4 = new Chopstick("4");
        Chopstick c5 = new Chopstick("5");
        new Philosopher("苏格拉底", c1, c2).start();
        new Philosopher("柏拉图", c2, c3).start();
        new Philosopher("亚里士多德", c3, c4).start();
        new Philosopher("赫拉克利特", c4, c5).start();
        new Philosopher("阿基米德", c5, c1).start();
    }
}

@Slf4j
class Philosopher extends Thread {
    Chopstick left;
    Chopstick right;

    public Philosopher(String name, Chopstick left, Chopstick right) {
        super(name);
        this.left = left;
        this.right = right;
    }

    private void eat() {
        log.debug("eating...");
        double random = Math.random();
        Sleeper.sleep(random);
    }

    @Override
    public void run() {
        double random = Math.random();
        while (true) {
            // 获得左手筷子
            if (left.tryLock()) {
                try {
                    if (right.tryLock()) {
                        try {
                            eat();
                        } finally {
                            right.unlock();
                        }
                    }
                } finally {
                    left.unlock();
                }
            }
            Sleeper.sleep(random);
        }
    }
}

class Chopstick extends ReentrantLock {
    String name;

    public Chopstick(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "筷子{" + name + '}';
    }
}